A rotary actuator employing a strain wave reduction gear is generally constituted by one motor and one strain wave reduction gear as have been proposed in Patent documents 1 and 2. A reduction gear unit disclosed in Patent document 1 has a structure in which one motor and one cup-type strain wave reduction gear are linked in tandem. An actuator disclosed in Patent document 2 has a structure in which one motor and one silk hat-type strain wave reduction gear are linked in tandem.
On the other hand, an actuator, which is provided with two cup-type or silk-hat-type strain wave gearing devices driven by one motor, has been proposed in Patent document 3. This actuator is provided with two output shafts and is capable of outputting reduced-speed rotations that are reduced at different reduction ratios from the respective output shafts.